The present invention relates to a bone implant apparatus, and more specifically but not exclusively a spinal osteosynthesis device of the type including a bone anchorage element, a vertebral rod, and a connector for interconnecting the rod and the anchorage element such that the anchorage element is capable of being angularly oriented in a polyaxial manner relative to the rod.
U.S. Pat. No. 5,486,174 and EP-A-0612507 describe such devices in which the connector is constituted by two jaws which define a lateral recess for the rod and in which conical openings are provided for the passage of the bone anchorage element. The latter comprises a shank having a double screw thread, one end part of which constitutes a bone anchorage screw. The opposite threaded end part projects from the upper jaw to permit the clamping of the assembly of the parts by a nut which comes to bear against the upper jaw.
Provided between the two threaded parts of the anchorage element shank is a spherical shoulder which comes to bear against the conical wall of the opening of the connector.
In this device, as in other known spinal osteosynthesis systems, a single nut is used to clamp the anchorage element, the connector and the rod in a chosen position. Consequently, if it is desired to increase the spacing between two consecutive anchorage elements, for example in the treatment of spondylolisthesis or for restoring a discal height or recreating a lordosis it is in fact only possible to slightly incline the anchorage element, without obtaining the desired increase in the spacing.
One object of the invention is to provide a spinal osteosynthesis device so arranged as to easily permit such an adjustment of the spacing between two successive anchorage elements.
One form of the present invention is a unique bone implant device. A further form is a unique spinal implant apparatus. Still a further form is a unique spinal osteosynthesis method.
According to another form of the invention, the spinal osteosynthesis device comprises separate means, on one hand means for fixing the position of the connector in translation and in rotation on the rod and, on the other hand, means for independently clamping the bone anchorage element to the connector in the chosen angular position. Such a separation of the clamping means permits easily adjusting the position of the connector, and consequently of the bone anchorage element, in translation on the rod, relative to the neighboring bone anchorage element and therefore obtaining an improved correction.
Further objects, forms, embodiments, aspects, features, benefits and advantages of the present invention will be apparent to one of ordinary skill in the art from the following description and drawings.